Unproductiveness due to physical condition may be corrected by a variety of means, includ ing drainage, irrigation, tillage and by a judi cious system of cropping and the proper use of manures and fertilizers.
There are large areas of swamp, marsh or muck soils which prove highly productive when reclaimed. In reclaiming such soils the first essential is thorough drainage. This is not only necessary for the purpose of removing the ex cess of water, but to allow the free circulation of air in the soil, in order that the poisonous compounds which are usually present may be oxidized and thus rendered harmless, and that the processes of decomposition and nitrification so necessary to render plant food available in this class of soil may be set up. Paring and burning to a depth of 12 to 16 inches as prac tised in Ireland and in European countries, and the liberal use of manures and fertilizers may often be necessary in addition to drainage, since such soils are as a rule deficient in phosphoric acid and potash, and although composed almost entirely of organic matter they are often de ficient in available nitrogen. Lime and the bulky manures often exert a beneficial effect on the texture of the soils, rendering them more porous, and thus improving drainage and increasing aeration and nitrification. Liberal applications of wood ashes also improve the texture of the soil, correct acidity and favor nitrification, and at the same time furnish pot ash and phosphoric acid. An application of a mixture of kainit or muriate of potash with some cheap phosphate, such as fine-ground Florida phosphate, may be substituted for the ashes. The untreated mineral phosphates have been used with advantage on muck soils, the decomposing organic matter assisting in ren dering the phosphoric acid available.
There are large areas of sandy lands in different parts of the United States which are extremely deficient in plant food, but which prove very valuable for a variety of purposes, but especially for early crops, when they are properly managed. One of the first require ments of such soils is an increase of humus to improve their water-holding capacity. The most effective means which has been found for increasing the humus supply in such soils is the growing and turning under of green crops, preferably leguminous plants, which are nitro gen collectors. Moderate liming has also been found beneficial in many cases.
Methods of Three prin cipal methods are employed in studying the characteristics and requirements of soils, namely, (1) mechanical and chemical analysis; (2) experiments in lysimeters, pits, pots or boxes, and (3) field experiments. The nature of the methods pursued in the chemical inves tigation of soils has already been indicated. The object of mechanical analysis is to separate the soil into particles of different degrees of fineness so that a basis may be secured for judging of the physical properties of the soil. Mechanical analysis as ordinarily practised separates a soil into what is termed skeleton (consisting of coarse particles like gravel and coarse sand larger than 0.5 millimeter in size) and fine earth, which includes all particles passing a sieve with meshes 0.5 millimeter in diameter. The fine earth is further separated into some six different grades, ranging from medium sand with particles 0.25 to 0.5 milli meter in diameter, through fine sand, silt, to clay, the particles of which are less than 0.005 millimeter in diameter. The methods of me chanical analysis which have been employed are of three classes: (1) hydraulic (Hilgard, Schone, Nobel) ; (2) sedimentation (Osborne, Schloesing, Knop), and (3) centrifugal. The methods which have been most commonly used in the United States are modifications either of Osborne's beaker (sedimentation) method or Hilgard's elutriator (hydraulic) method. The
physical examination of a soil also involves determinations of water-holding capacity, rate of percolation, capillary rise, hygroscopicity, adhesive rower, etc., for all of which ingenious methods have been devised.
Soil The soils of the United States have been studied to a considerable ex tent by the agricultural experiment stations, but while the work of the stations on soils has been quite varied and extensive it has not been systematic. The need for systematic and con certed study of soils has, however, been met by the organization and development of the work of the Bureau of Soils of the United States Department of Agriculture, which under takes the survey, mapping and study of soils on a scale never before attempted. In the in auguration of this work "it was recognized that differences of commercial value could be seen in the field from the character of the soil and from its relation to crops and vegetation; that it was quite possible to map these soil areas independently of the geology of the area or the exact chemical or physical cnaracter of the soil; that the proper course was to construct maps in the field, showing the area and dis tribution of the soil types; to explain as fully as possible from geological considerations the origin of the soil, and to have the soil chemist and physicist study the differences in the soil types.° Note is also made of climatic and economic conditions which may significantly affect the cropping practice. Extensive labor atory investigations supplemental to the field operations are conducted with a view to deter the chemical and physical properties of soils, improving methods and working out a more clearly defined classification.
In Germany elaborate soil surveys with ref erence to physical and chemical properties and productive and taxable value of the land have been made under government auspices by the 'Laboratorium fiir Bodenkunde° at Berlin. A systematic chemical survey of the soils of Bel gium was undertaken under the direction of the Gembloux Station. In France soil surveys have been undertaken by several of the depart ments, the soils being mapped with reference to their crop adaptations and fertilizer require ments. In Russia soil surveys have been suc cessfully prosecuted in several of the govern ments, and Japan has made considerable prog ress in work of this character.
Bibliography.— Risler,